The present invention relates generally to the spray-up technique for forming fiberglass articles in an open mold, and more particularly to an apparatus therefor which permits greater control of the amount of material dispensed during spray-up.
One procedure for forming fiberglass articles is known as open-mold spray-up, which involves spraying resin and catalyst together with chopped glass fibers continuously from a gun onto an open mold which delimits the outer surface of the article to be formed. Examples of articles formed by this procedure include boat hulls and wind fairings for trucks.
It has been a problem since the advent of the spray-up technique that a relatively high level of skill needs to be achieved by the operator through experience with the spray-up gun before he can produce consistently uniform articles. The operator needs to learn to spray the material onto the mold by starting at a particular point and moving the gun evenly at a particular speed and in a particular pattern, while holding to a certain overlap of the spray pattern. Having mastered the foregoing, he must also learn to gauge by sight and by a sense of elapsed time when a sufficient amount of material has been applied to the mold without exceeding the desired amount. If the amount of fiberglass material applied is too little, the product may fail to meet its design objectives. If the amount of fiberglass applied is too great, the part may again fail to meet the design objectives; but even if the part is acceptable, there will have been a waste of expensive materials which reduces the profitability of the venture.
It has been observed that even a skilled operator can only maintain a tolerance of about 10% of the design weight of the article using only his natural sensory skills. Furthermore, to train a new operator to the point where he can achieve the level of skill described above requires a matter of several weeks, during which time much production time is lost and much material is wasted. As a result, the spray-up fiberglass industry is undesirably dependent on those individual workers who have achieved the necessary skill level.
It would be desireable to provide an improved spray-up apparatus which would enable skilled workers to repeatedly produce spray-up fiberglass articles in open molds while maintaining a consistent unit weight with a smaller percent tolerance than was heretofore possible.
Furthermore, it would be desireable to provide such an improved spray-up apparatus which would reduce the level of skill necessary to produce acceptable articles, thereby enabling new operators to be trained in a lesser amount of time.
One way in which the operator can be assisted in producing articles of consistent weight is the provision of a meter which measures a cumulative amount of dispensed resin and which alerts the operator when the desired amount has been dispensed. A known commercially available digital resin meter includes an optical sensor attached to the pump shaft of the resin pump which sends pulses to the meter as the pump moves. The meter counts the pulses and closes an electrical circuit when a preset number has been reached. This circuit may be used to ring a bell, turn on a light, or close an air line valve to an automatic gun.
One disadvantage of the above-described meter is that it is located remotely from the operator, generally proximate the pump itself. For this reason, the operator cannot directly view a readout of the numerical display during operation of the spraygun, but must depend upon the alarm circuit to inform him when the desired number has been reached. This necessarily requires that the desired number be preset at the meter at a location away from the operating position. The operator must therefore return to the meter after spray-up of each article to reset the meter, and to change the preset number in the event that an article of a different weight from the just completed article is to be sprayed-up.
Merely relocating the aforementioned meter to a position proximate the operator is not feasible because of the harsh environment in the vicinity of the spray-gun operating position. Stray resin, catalyst and chopped fiberglass would soon coat the meter, obscuring the numerical readout. Furthermore, the chemicals used as components of the fiberglass articles and the solvents used for clean up would be harmful to electronic circuitry and quickly result in the failure of the unit.
The problems associated with the known meter discussed above are solved by the present invention.